[PATCH v1 1/1] Kernel Config to make randomize_va_space read-only.

["Lan Zheng (lanzheng)" <lanzheng@cisco.com>]

From ba2ec52f170a8e69d6c44238bb578f9518a7e3b7 Mon Sep 17 00:00:00 2001
From: lanzheng <lanzheng@cisco.com>
Date: Tue, 23 Feb 2021 22:49:34 -0500
Subject: [PATCH] This patch adds a kernel build config knob that disallows
 changes to the sysctl variable randomize_va_space.It makes harder for
 attacker to disable ASLR and reduces security risks.
 
Signed-off-by: lanzheng <lanzheng@cisco.com>
Reviewed-by: Yongkui Han <yonhan@cisco.com>
Tested-by: Nirmala Arumugam <niarumug@cisco.com>
---
 kernel/sysctl.c  | 4 ++++
 security/Kconfig | 8 ++++++++
 2 files changed, 12 insertions(+)
 
diff --git a/kernel/sysctl.c b/kernel/sysctl.c
index c9fbdd848138..2aa9bc8044c7 100644
--- a/kernel/sysctl.c
+++ b/kernel/sysctl.c
@@ -2426,7 +2426,11 @@ static struct ctl_table kern_table[] = {
                .procname       = "randomize_va_space",
                .data           = &randomize_va_space,
                .maxlen         = sizeof(int),
+#if defined(CONFIG_RANDOMIZE_VA_SPACE_READONLY)
+               .mode           = 0444,
+#else
                .mode           = 0644,
+#endif
                .proc_handler   = proc_dointvec,
        },
 #endif
diff --git a/security/Kconfig b/security/Kconfig
index 7561f6f99f1d..18b9dff4648c 100644
--- a/security/Kconfig
+++ b/security/Kconfig
@@ -7,6 +7,14 @@ menu "Security options"
 
 source "security/keys/Kconfig"
 
+config RANDOMIZE_VA_SPACE_READONLY
+       bool "Disallow change of randomize_va_space"
+       default y
+       help
+         If you say Y here, /proc/sys/kernel/randomize_va_space can not
+         be changed by any user, including root, this will help prevent
+         disablement of ASLR.
+
 config SECURITY_DMESG_RESTRICT
        bool "Restrict unprivileged access to the kernel syslog"
        default n
--